Rescuers in Iran are sifting through tons of rubble for survivors after a devastating earthquake hit the north-west of the country.

The interior ministry has revised the number of people thought to have died to 230, down from more than 500.

Iranian Red Crescent officials said about 25,000 people had left homeless by the tremor, measuring at least 6.0 on the Richter scale, which was centred around the town of Bou'in-Zahra, in northern Qazvin province.

A BBC correspondent in the region says many houses were single-storey mud and stone dwellings, so the process of searching for survivors should not be too protracted.

US President George W Bush has offered to send humanitarian aid, despite having branded the country as part of a worldwide "axis of evil", allegedly sheltering terrorists and promoting nuclear proliferation.

"Human suffering knows no political boundaries," said Mr Bush. "We stand ready to assist the people of Iran as needed and as desired."

However, our correspondent says Iran it unlikely to feel the need to take up such offers.

Villages wiped out

There have been more than 20 aftershocks since the earthquake struck at 0730 local time (0300 GMT) on Saturday, and seismologists have warned of the risk of more tremors over the next few weeks.

The quake was felt across a wide area including the provinces of Gilan, Tehran, Kurdestan, Zanjan and Hamedan, the official Irna news agency reported.

The sad task of burying the dead is under way

The Red Crescent said nearly 100 villages were badly damaged or destroyed.

Most of the deaths occurred in Bou'in-Zahra, where six villages were devastated, according to Irna.

In the tiny village of Abdareh, about 225 kilometres (140 miles ) west of Tehran, 40 homes collapsed and at least 20 people were killed.

About 80 people were killed in the Qazvin village of Kisse-Jin, the Red Crescent said, while about 40 people were killed in the village of Garm Darreh, in Hamedan.

A government official in Qazvin said 177 bodies had so far been pulled from the debris.

Maryam, a teenager who lost her mother, sister and two nieces, in Esmailabad, where 38 people died, said: "The ground started to shake and we wanted to run away but we couldn't."

State television showed images of dust-covered villagers in the Avaj district of Bou'in-Zahra crying and kneeling in the ruins of their houses.

Digging by hand

Tehran radio said tents had been set up to provide shelter for the homeless, but they are already reported to be in short supply.

The Red Crescent has brought helicopters and teams of sniffer dogs to help search for survivors, but most of the rescue work is being done by villagers themselves.

Civilians have been digging through debris with shovels and by hand.

Iranian President Mohammad Khatami has issued a message of condolence and declared three days of mourning in the provinces.